The formation of brittle microstructures around the fusion line in dissimilar welds has required a deeper microstructural analysis in this region. The study becomes more relevant when these welds are used in environments that facilitate hydrogen embrittlement. The present work aims to characterize the microstructure and hardness at the diluted zone interface in joints welded with dissimilar materials. Aiming for a better efficacy in the microstructural characterization of this zone, samples of both normal cross-section (NCS) and section with slope were used, according to the low-angle microsectioning (LAMS) technique, which allows a greater amplification of partially mixed zones (PMZs). The results indicated the diffusion of carbon from the heat-affected zone (HAZ) towards the fusion line which, in combination with other alloying elements, form highly brittle carbides. In turn, the hardness of the base metal and the HAZ was reduced after post weld heat treatment, whereas in the weld metal an opposite behavior was observed. The dissimilar interface was promising for applications in environments facilitating hydrogen embrittlement, especially regarding the characteristics of zone Φ.

This work consists of the study of the surface and Hardness properties of epoxy/quasicrystal (QC) composites. The composites had volumetric proportions of 1%, 10%, 20% and 30%, where the comparison was made between the composites and the pure epoxy resin. Techniques of Shore D Hardness, Thermogravimetric Analysis Techniques, Roughness Test, Contact Angle Analysis and Scanning Electron Microscopy (SEM) were used. Wettability test allowed to analyze the surface of the composite under the influence of two liquids: saline water and paraffinic oil. Regarding the composite and the pure resin, the contact angle increased when the liquid used in the test was saline water and decreased when exposed to paraffinic oil. It could be ensured that this small variation of the contact angles in relation to the increase of the composition occurred due to the influence of the roughness. In relation to saline water, the roughness has operated in order to prevent the liquid from spreading on the composite. As for paraffinic oil, it influenced in an opposite way, absorbing the oil and reducing the angle formed. When analyzing the pure quasicrystal, the effect was contrary to that of the composite: when it was exposed to saline water the contact angle decreased, on the other hand when exposed to paraffinic oil the resulting angle increased. This effect is related to the low polarity of the Quasicrystal, which when exposed to an apolar liquid tends to repel, thus forming a greater contact angle. Through this study it is concluded that it was possible to obtain a composite QC/Epoxy with greater hardness and still maintain its surface characteristics.

Steel plates have been coated by Al-based quasicrystal obtained by atomization from the liquid state and sprayed using a high-velocity oxygen-fuel flame torch. Static and sliding contact experiments were carried out in order to assess on the one hand the mechanical properties of the quasicrystal and on the other hand the friction and related properties such as wear and resistance to scratch. Besides these conventional properties, indentation experiments reveal the porous nature of the thick coating. Scratch test experiments pinpoint the low elastic recovery of the sample (despite a low plastic deformation at high loads). Pin on disc experiments reveals the abrasive nature of the coating. In the end, the friction properties of this type of coating appear excellent in comparison to many state-of-the-art surface layers. The talk will summarize such findings and will compare them to solutions most frequently used in mechanical devices.

After gas atomization, a quasicrystalline powder based on aluminium was used to prepare a thick coating by high-velocity oxygen-fuel flame torch spraying. This layer was deposited on top of a bond-coat layer on a steel plate. A post-spraying annealing treatment turned the two layers to their stable state, a γ-brass crystal and an icosahedral quasicrystal, respectively. The projection parameters were selected in such a way that the coating behaved like a self-lubricating material, which offered very good wear resistance (duration of pin-on-disk tests superior to 5 km with negligible material loss) and low friction (µ ≤ 6% against sintered tungsten carbide), in contrast to the state of the art. This property was achieved thanks to, on the one hand, excellent bonding to the substrate via the bound coat, and on the other hand, presence at the boundaries between quasicrystalline flakes of a mixture of both threefold and fourfold coordinated carbon originating from spray processing. Application to hard materials used in mechanical devices is appealing, especially because soft, lubricating additives may not be needed, thus considerably increasing the lifetime of the devices and reducing waste of materials.

This work summarizes an attempt to estimate the surface energy of the stable, icosahedral Al–Cu–Fe quasicrystal (i-ACF hereafter). To this end, samples of i-ACF were prepared by sintering a powder produced by ball milling and heat treating a master ingot of composition Al59Cu25.5Fe12.5B3 (at.%), icosahedral lattice structure, and containing negligibly small amounts of contaminating crystalline phases. This powder was then sintered in the shape of a cylinder appropriate for pin-on-disk tests in ambient air. Variable amounts of either Sn or Bi were added to the powder prior to sintering. These elements do not dissolve in the quasicrystal and form small pockets of pure Sn or Bi that are either isolated or percolating, depending on the added volume of metal. Analysis of pin-on-disk data deduced from tests performed at room temperature allows us to conclude that the surface energy of the quasicrystal itself falls between the respective surface energies of the pure metals: γBi ≤ γQC ≤ γSn or 0.5 ≤ γi-ACF ≤ 0.8 J/m2.

An investigation was made of hybrid microwave-assisted sintering of dental porcelains, using five commercial ceramic frits employed in the production of dental porcelains. The powders were characterized, transformed into prismatic test specimens, and subjected to conventional and microwave sintering. Microwave sintering was performed at a frequency of 2.45GHz, using a susceptor material and in the absence of vacuum. The apparent density and apparent porosity of the sintered samples were characterized based on the Archimedes principle. They were also analyzed by X-ray diffraction (XRD) and scanning electron microscopy (SEM), and their flexural strength and microhardness were determined by the Vickers method. The powders, which showed a broad particle size distribution with a high fraction of particles of dimensions larger than 30μm, were composed of amorphous phase and leucite particles. Microwave sintering yielded ceramic bodies whose apparent porosity (t-test, p<0.05) was the same or very similar to that of the conventionally sintered samples, while the apparent density (t-test, p<0.05) of most of the microwave sintered samples was the same or slightly lower. Although the microwave sintered samples showed larger average pore sizes (t-test, p<0.05), four of the five samples used in this study showed the same flexural strength (t-test, p<0.05) and all the ceramics under study showed the same surface microhardness (t-test, p<0.05).

Summary Biomedical Ultra‐High‐Molecular‐Weight Polyethylene (B‐UHMWPE) is widely used in orthopaedics as a biomaterial because of its mechanical properties and biocompatibility. However the adding of vitamin antioxidants can influence the inflammatory process. Thus, the objective of this study is to evaluate the influence of adding ascorbic acid (vitamin C) at different concentrations to the B‐UHMWPE matrix, using for this purpose the Scanning Electron Microscopy (SEM) and Differential Scanning Calorimetry (DSC) analyses. The vitamin C was mixed with B‐UHMWPE in concentrations of 0.5, 1.0 and 2.0%wt and the molding was performed with a 10MPa load at 160 °C for 6min.The fracture surface of cross‐sectional area of B‐UHMWPE modified with vitamin C showed that the vitamin is present in the polymer matrix in the form of small agglomerates, being an indication that there was no fusion of the vitamin C during the processing step. Using the technique of differential scanning calorimetry it was observed that the melting temperature remained constant as well as the crystallisation temperature, but there was a small variation in crystallinity with the addition of vitamin C. From this study, we conclude that the presence of vitamin C (ascorbic acid) did not alter the thermal properties of crystallisation and melting of B‐UHMWPE.

Room temperature photoluminescence (PL) of SrSnO3: Fe3+ perovskites synthesized by the polymeric precursor method was evaluated. The amount of carbonate decreased with increasing temperature, as shown in the XRD patterns and the IR spectra. According to the IR spectra, the splitting of the ν1 band indicated that clusters with different symmetries were formed, especially in samples doped with 20 mol % of Fe3+. PL at different regions was observed, indicating that different defects are present in the structure. For samples calcined at 400 ºC, a yellow emission was observed indicating a higher short-range disorder. Increasing the calcination temperature to 700 ºC led to a change in the emission region to green or blue. This behavior was assigned to a higher short range ordering also suggested by the increase in the band gap value. Keywords: Fe(III), infrared spectroscopy, pechini, perovskite, photoluminescence, PL, polymeric precursor method, raman spectroscopy, short- and long-range order, SrSnO3, strontium stannate, UV-Vis spectroscopy, X-ray diffraction.

Nanostructured iron (III) oxide (α-Fe2O3) was synthesized using Fe(NO3)3, PEG and different bases (NaOH and NH4OH) as precursors via hydrothermal microwave method. Several experimental techniques were employed to formulate an optic-structural model. The results proved the efficient synthesis of α-Fe2O3 and demonstrated that the material’s behavior could be tuned using different conditions in the reaction. Ultra fast synthesis (1 min) of α-Fe2O3 was obtained when NH4OH was used as the alkalinizing agent. Evaluating the short- and long-range order before and after microwave heating was possible. PEG and the alkalinizing agent fundamentally influenced the material morphology; three different particle shapes were observed: hexagons (NaOH with PEG), rods (NaOH without PEG) and spheres (NH4OH with PEG). Keywords: α-Fe2O3, ammonia, hematite, field emission scanning electronic microscopy, infrared spectroscopy, iron (III) oxide, microwave-assisted hydrothermal methods, morphology, PEG, sodium hydroxide, Raman spectroscopy, UV-Vis spectroscopy, X-ray diffraction

The quasicrystals materials possess a combination of unusual properties, since they present a long range ordered atomic structure, which is not periodic. Because of this, these materials have been object of study of many researchers in the last few years. Currently, the research is focused on determining new techniques able to produce these materials in a large scale, as well as finding new utilities. One of the ways to do so, is to use quasicrystals as coating; another way is the fabrication of composites. In this paper, aluminum composites with the strengthening of quasicrystalline particles from the alloy Al59,2Cu25,5Fe12,3B3in volumetric fractions of 6% to 20% were developed by high energy ball milling. The powders obtained by mechanical alloying was compacted at 300MPa, sintered and submitted to micro hardness tests. The characterization was made by X-ray diffraction and SEM. In the grinding we used a 2² factorial design with factors time and speed, and the hardness of composite as response. The specimens had an average hardness of 25.75GPa for reinforcement with 6% QC and 34.75GPa for reinforcement of 20% QC.

The composite studied here consisted of a geopolymer matrix reinforced with quasicrystal powders. Quasicrystals are complex metal alloys with atypical structures. Due to their physical, mechanical and surface properties, quasicrystals have been widely studied. Nowadays quasicrystalline powders are proposed to be incorporated in ductile matrices. The geopolymers are inorganic polymers with excellent thermal performance and interesting adhesive properties. The quasicrystalline alloys were prepared by induction melting the constituents under argon atmosphere in a water-cooled copper crucible. In this work the adhesion of composites with 5, 10 and 15% of quasicrystal powder in aluminum joints was investigated. In addition, the influence of the curing time was taken in to account and tests were performed in samples with 7 and 28 days of cure. The results indicate an improvement in adherence with the inclusion of quasicrystal. The best adherence was obtained when the curing time was 28 days.

Quasicrystalline materials have unique properties such as high hardness, excellent surface properties, good resistance to oxidation and corrosion and low electrical and thermal conductivities. These materials can be obtained by conventional methods of metallurgy. However, quasicrystals are quite weak and this characteristic complicates their use in the form of billets for the manufacture of mechanical components. For this reason, the evaluation of mechanical properties of quasicrystalline materials using conventional methods, such as tension, compression, fatigue, among others, is not feasible. One method to evaluate the mechanical properties of quasicrystals is through instrumented indentation, once it is a very efficient tool for the calculation of properties such as hardness, fracture toughness and modulus of elasticity. The latter was the property studied in this work and that it is an important design criterion for the manufacturing of quasicrystalline alloys for their use in industry.

The geopolymer although being a recently discovered material, it is already present in many industrial sectors. This range of applications is due to the commitment of the scientific community to understand and manipulate the material, seeking a contribution in this regard, it has produced geopolymer matrix composites with quasicrystalline and reinforcement, Al62,2Cu25,5Fe12,3 in the proportion of 10%, 20% and 30% by volume. These composites were obtained by manual production and heat treated at 400 º C for two hours. The characterization was made with the aid of scanning electron microscopy (SEM) and x-ray diffraction (XRD). Diffractograms of composites without heat treatment showed characteristic peaks of the phases present in the matrix and reinforcement. For the composites with heat-treated, it was observed that besides the phases mentioned above the presence of diffraction peaks possibly associated phase silica sodium aluminate. The composite showed good interface quasicrystal / geopolymer, showing the existence of a phase with lamellar morphology in the treated material.

This paper presents a study on microstructure, elasticity modulus and electrochemical behavior of Ti-26Nb, Ti-26Zr and Ti-26Ta binary alloys obtained in an induction furnace equipped with a water cooled copper crucible which can promote levitation of the moltem alloys. The microstructures and eletrochemical behavior were investigated by means of X-ray fluorescence spectroscopy, X-ray diffractometry, optical microscopy, microvickers hardness, open circuit potential, corrosion potential and polarization resistance. The results revealed that the difference in nominal chemical composition related to contamination was extremely low, which indicates that this melting technique is highly appropriate for obtaining contaminant-free titanium alloy. The addition of niobium was very favorable for obtaining near-β alloy with a low elasticity modulus. Additionally, alloy Ti-26Nb presented the best corrosion resistance combined with low elasticity modulus.

Chromium and cobalt oxides are widely used in the manufacture of industrial pigments. In this work, the Co(Co2−xCrx)O4 powders with different chromium concentrations (x=0, 0.25 and 1) were synthesized by the polymeric precursor method, heat treatment between 600 and 1000°C. These powders were characterized by X-ray diffraction, infrared spectroscopy, colorimetry, UV–vis absorption and X-ray photoelectron spectroscopies. Even with the addition of chromium, the XRD patterns revealed that all powders crystallize in a single spinel cubic structure. The spinels with higher cobalt amount, Co(CoCr)O4 and Co(Co1.75Cr0.25)O4, displayed a dark color, without the Co3+ reduction observed in Co3O4 between 900 and 950°C. The spinel with higher chromium amount, CoCr2O4, was green. The colors were directly related to the occupation of tetrahedral and octahedral sites by the chromophores, as well as to the different oxidation states of chromium and cobalt. The different optical band gap values estimated from UV–vis spectra suggested the existence of intermediary energy levels within the band gap. X-ray photoelectron spectroscopy confirmed an increasing presence of Co(III) and a decreasing amount of Cr(VI) with cobalt enrichment.

This study evaluates the margin of a nanofill, a nanohybrid, and a conventional microhybrid composite in restorations in occlusal cavities of posterior teeth after 12 months. Forty‐one patients, each with three molars affected by primary caries or the need to replace restorations, participated in this research. The teeth were restored with a nanofill (Filtek Z350), a nanohybrid (Esthet‐X), and a microhybrid as a control (Filtek Z250). Ten patients were selected randomly, and the three restorations were molded with a low‐viscosity polyvinyl siloxane material. The molds were poured with epoxy resin, gold‐sputter coated, observed by scanning electron microscopy, and classified as: “perfect margin,” “marginal irregularity,” “marginal gap,” “marginal fracture,” or “artifact.” For statistical analysis, the Wilcoxon and Friedman nonparametric tests and paired‐samples t ‐test were used (significance level of 5%). The performance of the three materials was compared after 1 week and 12 months. No statistically significant differences were detected for all criteria ( P > 0.05). When each composite was compared over time, statistically significant differences were found for the criterion, perfect margins (Esthet‐X and Filtek Z350, P < 0.05). The materials performed satisfactorily over the 12‐month‐observation period, but all composites under investigation showed a certain amount of deterioration relating to marginal quality over time. Microsc. Res. Tech. 74:23‐27, 2011. © 2010 Wiley‐Liss, Inc.

The effect of cyclic deformation on the stability of superelasticity was investigated for the Cu-12wt%Al-0.5wy%Be alloy. The loading and unloading cyclic tensile tests were performed at room temperature and at 57oC with the maximum constant strain of 4%. The effect of holding the applied strain for a period of time on the superelastic properties was also investigated. It was confirmed that the total volume fraction of the retained martensite changes with time after unloading cycle, leading to the reduction of the residual strain. Additionally, the residual strain increases as the loading cycle of the applied strain is kept constant for a period of time.

Polycrystalline specimens of Cu-Al-Be shape memory alloys were homogenized at 1123K during 12h and water-quenched at room temperature. The phase transformation temperatures were determined via optical microscopy technique, using a cooling/heating device attached to the microscope stage. Comparisons have been made with data obtained via differential scanning calorimetry. The data show that the former technique can be successfully applied to the determination of typical transition temperatures occurring in shape memory alloys. As far as sample related problems are concerned, the former technique can also represent an advantageous alternative over the latter given the fact that the analyses can be performed in more representative area. The M-f and A(s) temperatures precise detection depend on the chosen resolution of the optical microscope.